test: use helpers for unions and scalar tests

[thisisnithin]

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Motivation and Context

Refactors the tests to use existing helpers for normalization and federation

Checklist

• [ ] I have discussed my proposed changes in an issue and have received approval to proceed.
• [ ] I have followed the coding standards of the project.
• [ ] Tests or benchmarks have been added or updated.
• [ ] Documentation has been updated on https://github.com/wundergraph/cosmo-docs.
• [ ] I have read the Contributors Guide.